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Laboratory Diagnosis

The diagnosis of giardiasis is established by identifying cysts or trophozoites in stool specimens. Permanent stained smears are more sensitive than wet preparation examinations in detecting Giardia cysts or trophozoites. However, the excretion of the parasites may be intermittent and the diagnosis can be missed even on repeated stool examination. In these patients, duodenal aspirates obtained after intubation or by using the Entero-Test capsule should be examined; if these contain no G. lamblia and giardiasis is still suspected clinically, examination of serial sections and impression smears from intestinal biopsies may be necessary. Impression smears of mucosa are one of the most sensitive methods of detecting giardiasis, whereas histologic evaluation of intestinal biopsies can be difficult. The diagnosis can also be made by endoscopic brush cytology of the duodenum ( Marshall et al). In a study by Kamath and Murugasu of children in whom the organism was identified on small intestinal biopsy, G. lamblia was found in the duodenal aspirate of only 75% and in the stool of only 50%.

ELISA (enzyme-linked immunosorbent assay) is as sensitive as the microscopic examination of wet preparations since it detects Giardia antigen in stool samples. Although usually not clinically useful, serum antibodies against Giardia can be detected by serological techniques such as indirect fluorescent antibody tests (IFA), ELISA, and radioimmunoassay (RIA).

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